In this paper, the approximate analysis of the low aspect ratio wing is carried out, getting a new integral equation of the lifting surface being oblique in the plane of free stream in order to estimate the lift distribution on the wing with low aspect ratio. The bound vortices are herein assumed to be distributed over the wing surface that is considered as the lifting surface and hence the induced free vortex filaments extend over the infinite down. stream having reasonable small angle to the wing surface. Applying this integral equation to the extreme case of the lifting surface, it is shown that Munk's Integral Equation is derived in case of the infinite span, and on the other hand, in case of the infinite chord wing the same result is given as that being obtained by Newton's momentum theory. The integral equation identical with that by Prandtl is further derived from the author's equation, putting aspect ratio high as the approximate treatment.